Influenza-related mortality trends in japanese and american seniors: Evidence for the indirect mortality benefits of vaccinating schoolchildren

Abstract

Background: The historical Japanese influenza vaccination program targeted at schoolchildren provides a unique opportunity to evaluate the indirect benefits of vaccinating high-transmitter groups to mitigate disease burden among seniors. Here we characterize the indirect mortality benefits of vaccinating schoolchildren based on data from Japan and the US. Methods: We compared age-specific influenza-related excess mortality rates in Japanese seniors aged ≥65 years during the schoolchildren vaccination program (1978-1994) and after the program was discontinued (1995-2006). Indirect vaccine benefits were adjusted for demographic changes, socioeconomics and dominant influenza subtype; US mortality data were used as a control. Results: We estimate that the schoolchildren vaccination program conferred a 36% adjusted mortality reduction among Japanese seniors (95%CI: 17-51%), corresponding to ~1,000 senior deaths averted by vaccination annually (95%CI: 400-1,800). In contrast, influenza-related mortality did not change among US seniors, despite increasing vaccine coverage in this population. Conclusions: The Japanese schoolchildren vaccination program was associated with substantial indirect mortality benefits in seniors.